Television system



Dec. 28, 1943. TEAL 2,337,578

TELEVISION SYSTEM Filed July 31, 1941 2 Sheets-Sheet 1 FIG.

DIRECT/0N or SCANNING 0F LINE or LIGHT 1 SUBJECT 55 FIG. 6 if "///////11/// 30 I 9/ #4 42 2/ W ///////////7///,, F IG. 2 2: Wm mm 3 .90 42 30 r0 RES/SHAKE amscnmv OF FIG. 3 0 SUBJECT sung/ o; LINE 6o E L E C TRON BEAM FROM L I/VE SOURCE INVENTOP a/r. TEAL A T TORNEV Patented Dec. 28, 1943 TELEVISION SYSTEM Gordon K. Teal, Mountain Lakes, N. 1., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporationof New York Application July 31, 1941, Serial No. 404,767 2: Claims. (c1. its-1.2)

This application relates to electron discharge devices and more specifically to television systems employing such devices.

' It is an object of this invention to provide novel ,electro-optical systems each utilizing a, moving sheet of light for scanning an object line-by-line. Such scanning will be hereinafter referred to as flying line scanning.

It is a further object of this invention to provide novel electronic means for forming a scanning line of light. 7

Several difliculties have impeded the immediate development of a satisfactory electronic two-way television system. For example, it is very desirable' to use either a camera tube because of its large storage of charge or a combination of flying spot scanning of the subject by fluorescent light from a projection cathode ray tube with a multiplier photocell. The camera tubes now in use, however, require too great an intensity of light on the subject and current methods of using such flying spot scanning place very severe requirements on the rapidity of the decay v of the fluorescence of screen material.

In the present invention these difllculties are greatly ameliorated without elimination of the use of a storage type of camera tube. By recourse to a flying line of light from a cathode ray tube of this invention in combination with a camera tube having in it a one-dimensional mosaic, it becomes practical to construct tubes which give a storage of charge which as pointed out hereinafter is greater than that occurring in present camera tubes in an equal interval of time due to the reduction of spurious signals caused by the secondary emission from the mosaic. The use of the line light source in combination with such a camera tube also reduces the stringency of requirement on the rapidity of decay of the fluorescence of the screen material.

In one embodiment of the invention, shown v by referring to the following by way of example fOr' purposes of fllustration, a

television transmission ploying an electron camera tube having a onedimensional mosaic of conducting plugs supported in capacitative relationship to a common condenser plate. The subject is scanned in a vertical direction at rramefrequency by amoving, line or light. An image of the subject is focussed by a lens system drically curved photocathode the curvature of which is such as todirect, in cooperation with.

cylindrical electron from a vertical arc lens elements, all electrons in a plane parallel to the 'system is provided emonto a semitransparent cylinprovided and this of the photocathode is individual elements of the mosaic are scanned at line frequency by an electron beam from a cathode'ray gun at a voltage such that they are thereby driven to a less positive equilibrium potentiaL The television signal is taken of! the condenser plate by means of a coupling resistance. A special type of cathode ray gun for generating a moving line of fluorescent light is gun comprises a line source of electrons and cylindrical electron lenses for focussing' the electrons onto a line of the fluorescent screen. The linear sheet of electrons is deflected at frame frequency by means of a sawtooth wave applied to a pair of deflector plates.

In a modified arrangement, an electronic image of a spherically curved photocathode is formed on a diaphragm at the end of the flnal accelerating electrode and a slit in this diaphragm parallel to the flying line of light intercepts portions of the electronic image swept vertically across the slit in synchronism with the movement of the line of light. While only a line illuminated at a time, the sheet of electrons corresponding thereto is made to coincide with the slit by means of the vertical movement which is caused, for example, by magnetic coils.

' The invention will be more readily understood description taken in connection with the accompanyingdrawings forming a part thereof in which:

Fig. 1 shows a television transmitter in accordance with the invention;

Fig. 2 is an enlarged view of a portion of the electron target in of-Fig. 1; c

Fig. 3 shows apparatus for generating a moving line of light;

Fig. 6 is an enlarged view of another form of electron target.

Referring more specifically to the drawings, Fig. 1 shows, by way of example for purposes of illusthe tube shown in the system as-tight, however.

tration, 'a television system embodying certain principles of this invention. The system comprises means (shown in greater detail in Fig. 3) for producing a moving line of light l preferably for vertically scanning an object or field of tube l3 wherein-a television image current is formed and passed through resistance M in the external circuit thereof. The photocathode 2 is curved cylindrically. The resistance i4 is preferably connected to amplifying means and other appropriate apparatus (not shown) for transmitting a television signal to a receiving station.

The cathode ray transmitter tube |3 comprises an evacuated envelope-29 of approximately rectangular cross section in a plane perpendicular to the plane of the drawing, the longer dimension of the cross-section being in the direction perpendicular to the plane of the drawing, which envelope is separated by a linear mosaic electrode 2| and a diaphragm member 29 into a first cham ber 22 and a second chamber 23. The barrier between the two chambers 22 and 23 need not be In the first chamber 22 a photosensitive layer I2 is coated on the curved end of the tube and a plurality of accelerating electrodes 24, 25, 2B, 21 and 29 which constitute cylindrical lens elements (1. e. pairs oi. plates, each being longer than'the mosaic electrode and each of the plates of a pair being at the same. potential, or rectangular open-ended boxes, the dimension of each of which in the direction at right angles to the plane of the drawing is relatively long compared to the dimension in the plane. of the drawing and to the length of the mosaic) focus the electrons emitted from the photocathode |2 upon the linear mosaic target 2| through the aperture in the last accelerating member 28 which is preferably a diaphragm member with a slit aperture therein. The linear mosaic element 2| is preferably contained in a diaphragm member 29 which is incapacitative relation to each of the plugs 39 in the mosaic electrode 2|. of the photocathode 2 and the focussing action of the electrode elements 24 to 28, inclusive, which are placed at progressively accelerating potentials by connections to successive taps 3|, 32, 33, 34 and 35 of the potentiometer resistance 36 connected across the source of potential 31 (the photocathodebeing connected to the negative pole of said source), each of the electrons from the photocathode |2 regardless of its vertical position, is directed along a vertical are (that is, in an arc in a plane parallel to the drawing) to the one-dimensional mosaic 2|. In cases where the vertical focussing is not very sharp the elements of the mosaic can be made to have appreciable lengths in the vertical direction, which, however. is not objectionable. The image of the line of light on the subject 0 moves verticallyon the photocathode l2, resulting in the storage of charge on the mosaic element 2| during a line period.

Reference will now be made to Fig. 2 which 'shows, by way of example, an enlarged. crosssectional View of one form of linear mosaic elec- 1. comprises two parallel and separated strips 49 (See Fig. 2.) Due to the curvature adjacent metallic strips.

and 4| of insulating material, such as mica, hav- 76 ing apertures therein for the passage of two-sided conducting plugs 30. Between the insulating strips 40 and 4| is a. metallic layer 42 having apertures 43 therein corresponding with the apertures in the plates 40 and 4| but being larger so as not to make contact with the conducting plugs 30. As pointed out above, the mosaic target 2| is mounted within a slit aperture in the 'plate 29 which" acts as a common condenser plate to all of the conducting members 49, the plate 29 being connected through the output resistor 4 to the negative pole of the source of potential 44, the positive pole of which is connected to the positive pole of the source 31. The negative pole of the source 44 is preferably connected to ground and to the positive pole of a source 45, the purpose of which will be described more fully below.

The mosaic target 2| may be made, alternatively, by covering a mesh metallic screen with melted glass or other refractory material and then filling the holes with metal, or mosaics with narrower elements canbe made by stacking pieces of mica and metal 9| alternately as shown in Fig. 6. This method is much'simpler than the other methods. The structure shown in Fig. 6 may use the diaphragm 29 as the common capacity element for the metal pieces 9| or alternate pieces 9| may be connected together and to the resistance I4 and form the capacity element in this manner. In this latter arrangement the elemental charges are set up between Referring again to Fig. 2 the sides ii, of the plugs 30, facing the subject 0 are coated with suitable secondary emitting material, suchv as CsOAg, so that a positive charge is'left on the plugs 30, the electrode element 28 acting to collect the secondary electrons emitted from the sides h of the conducting members 30 when photoelectrons, which have been accelerated by the members 24 to 28, inclusive, strike these plugs.

In the chamber 23, means, such as the cathode 50, heated by a'heater or filament member 5|, and anodes 52, 53 and 54 are provided for generating a beam of primary electrons in and for focussing it upon the ends I; of the conducting plugs 30 of the mosaic target 2|. The electrodes 53 and 54 are preferably connected together and to ground. Ground is also made the potential of the positive pole of the source 45, an intermediate tap 46 of which is connected tothe anode 52 and the negative pole of which is connected to the cathode 50. Any suitable means may be used to supply current to the heater 5|. Means, such as the magnetic coils 55, 55 supplied with current of saw-tooth wave form cause the beam to sweep in a line perpendicular to the plane of the drawing across the faces f2 of the'conducting elements 30 to discharge the charges which have been formed between the conducting members 30 and the common electrode member 29 by the photoelectrons z' from the photosensitive target l2 impinging thereon. Secondary electrons (2'5 emitted from the surface 12 are collected by the collector electrode 54 which preferably comprises a ring coating around the inside of a portion of the walls of the chamber 23.

While any suitable means for producing a line of light perpendicular to the plane of the drawing'and which move in the direction indicated by the arrow in Fig. 1 may be'used, such as a mechanical optical device, preferably the moving line of light is generatedby a line of electrons scanning a fluorescent material, Such a means is shown in Fig. 3 wherein there is provided a .lected by the collecting electrode 28.

v assure cathode ray tube ID for generating a moving line of light In perpendicular to the plane of the paper and which scans the object or field of view in the direction of the arrow. The tube 60 preferably comprises a linear cathode 6|, a

shielding member 82 surrounding the cathode except for a slit aperture 63 in the face thereof adjacent the cathode 6|, cylindrical electron lens elements 64 and 65, a pair of deflecting plates ing, moves up and down the object in the directions indicated by the arrow. The cylindrical lens elements 64 and 65 may comprise pairs of plates having the same potential appliedto the plates of each-pair butwith the potential of the first pair being of a suitable ratio with respect to that ofthe second pair to form the stream of electrons into a line on the fluorescent screen 88. As an alternative th lens elements 64 and 65 may comprise tubes or boxes having rectangular cross-sections. Any suitable sweep circuit may be connected to the pair of plates 66', 61 to produce deflection of the line of light in a preferably vertical direction.

The system shown in Fig. 1 operates asfollows: A line of light is generated by any suitable means, such as by the cathode ray tube 60 shown in Fig. 3 and this line causes the subject or field of view 0. to be scanned vertically at lframe frequency, this frequency beiing determined by the frequency of the saw-toothed wave applied between the deflecting plates and 61 of the tube 60. An optical image of the portion being. scanned at each instant is focussed upon the curved photocathode I! by means of the lens system H. A sheet of electrons is generated at the photocathode l2 and because of its curvature which tends todirect the-photoelectrons towards the line of elements 30 and because of the electrode element 24 to -28 inclusive, no matter what the vertical height, this sheet i hits on the line of conducting elements 30 so as to give a storage of charge during the line period.

Due to the front faces in of. the elements 30 be .ing coated with a secondary-emitting material such as Cs-O-Ag, the rate of storage of charge is increased approximately ten times by secondary emission, the secondary current being col- After an element has been charged verypositive relative to the electrode 29 forming a common electrode of a capacity between it and all of the photoemissive elements 30 (and also with respect to the potential of the collecting electrode 54 for the secondary current is, from the faces f: of

the conducting electrodes 30) it is discharged by the electron beam is formed in the chamber 23.

. This beam is swept along the line in a direction perpendicular to the plane of the drawing by' means of. currents of saw-tooth wave form ap-.'

plied through the coils 55. This beam sweeps the line at line scanning frequency and drives the elements to a lesspositive equilibrium potential relative to the potential of the, last anode I4 in chamber 23. The television signal is generated across the resistance i4 connected between the electrode member 29 and ground (which is the potential of the ,last anode 54 of the electron gun system in a chamber 23) The advantages ot-the arrangement shown in Fig. 1 over various arrangements of the prior art,

may belisted as follows: (1) his astorage method. thus being an improvement over the "spot scanning system using mechanical means shown in Patent 2,113,254 issued Aprfl 5, 1938 to Frank Gray; (2) the average illumination of the subject can be kept low due to the flying line of light scanning feature; (3) it is a completely electronic system when the arrangement shown in Fig. 3 for generating the flying line of light is used; (4) the system avoids unfavorable optical systems inasmuch as it is not necessary to use cylindrical optical lenses; (5) the photoelectron current is saturated because the photocathode I2 is continuously negative with respect tothe accelerating members 24 to 28, inclusive; (6) because of secondary emission, multiplication of the charge is obtained; (7) because of the fact that only a single line of elements i used,

I it is feasible to construct the mosaic by simple mechanical methods such as by. stacking alternate layers of metal and mica; and (8) the' trouble from spurious signals is minimized because the stacked layer line mosaic can readily be made to retard the return to the mosaic of 2 secondaries released-by the scanning beam by connecting every other'metal plate M to the re sistance l4 thus. making these plate negative with respect to the alternate plates which are charged positively by the accelerated photoelectrons, and because the secondary current from a given element during discharge increases from a small value to is =iorather than decreasing from a high value to a value where i= =io, thus reducing the secondary electron spray for some signal strengths.

A comparison of the maximum allowable decay period of the fluorescentmaterial used'in the.

lines in thepicture with a 1 to 1 aspect ratio, the

, upper curve being for flying line scanning and .m the lower curve being for flying spot scanning with photocell pickup. vFrom these curves it appears that there is a much greater choice of fluorescent materials in using the flying line scanning method rather than the other andi the chance of selecting a material with suitable brilliant radiations in regions of the spectrum to which the subject's eyes are relatively insensitive, i. e.. the red and blue portions of the spec- 'trum, is greatly enhanced. The choice of fluorescent materials can also-be made much easier when a flying line of light is used with an image dissector type of camera tube in which an electron image of the line is swept across the defining square aperture by horizontal and frame sweeps in exact synchronism with the flying line of fluorescent light focussed on the subject.

Fig. 4 shows a modified arrangement. In this figure the tube has a'circular cross section as'to focusan electronic image of the photocathode which .in this case is spherically curved on the end .10 of a final accelerating electrode II, the electrodes 94. and 96 being 10 cylindrical members which act as spherical electron lens elements. These three electrodes are followed by a diaphragm electrode 12 and the long tubular accelerating anode II. The rest of the elements inthe tube 80. i. e.. the electron gun 14 elements in'the chamber 23, are similar to the correspondingly n'umbered elements of the arrangement shown in Fig. 1. The tube has been shown cut at the line X-'---X of Fig. 4 but it is to be understood that all portions to the right of this line are similar to those elements shown to the right of the line XX in the arrangement of Fig. 1, it being understood, however, that the shapes of the envelopes may be difierent in the two cases. In the arrangement of Fig. 4, the slit 13 in the diaphragm III of the electrode element H is'parallel to the flying line of light and hence the electron stream generated thereby and focussed upon the diaphragm 10. The entire electronic image (actually only a line at a time) is swept vertically across the slit 13 in synchronism with the movement of the line of light by means of current waves applied to the coils 14 indicated schematically on the drawing. By this arrangement the slit is at each instant filled with a line of electrons representative of the line of the image being scanned by the line of light at that instant. Thus, an electron image representative of a line'of the object is caused to strike the ends'fi of the elements 30 of the mosaic target 2| every line scanning interval where it is scanned by the electron beam in gen- .erated in the chamber 23 as described above in linear target regardless of what part of the cathode is illuminated by the moving sheet of light reflected from the object, and means including said linear target for setting up image currents which may be used to reproduce an image of the 7 object.

connection with the arrangement shown in Fig.

described in connection with Fig, 1.

It is obvious that the tubes shown in Figs. 1, 3 and 4 may be used in a non-mechanical system with any other non-mechanical generator of flying spots or lines of light, such as the .supersonic light valve. The tubes of this invention may be used advantageously in scanning motion picture films which, for any reason, "must be moved intermittently as is vdone in most film projectors.

Various other modifications may be made in the embodiments above described without departing from the spirit of the invention, the scope of which is indicated by the appended claims,

What is claimed is:

1. In combination, means for illuminating s'uccessively various linear portions of an object with a moving sheet of light, a photoelectric cathode, means for projecting an image of those portions of said object which are successively illuminated upon saidcathode for generating a moving sheet of electrons having a cross-section corresponding in shape to the cross section of the sheet of light, an electrode member, means comprising electron deflecting means for causing said sheet of electrons to impinge upon said electrode member, and means including saidelectrode member for setting up image currentswhich may be used to reproduce an image of the object.

2. In combination, means'for illuminating successively various linear portions of an object with a moving sheet of light, a curved photoelectric cathode, means for projecting an image of said object so illuminated upon said cathodeto generate a moving sheet of electrons, a linear target for said electrons, means for setting up a focusing field between said cathode and said target of such a nature that the sheet of electrons reaches said 3. In combination, means for illuminating su'ccessively various linear portions of an object with a moving sheet of light, and an electron discharge device including aphotoelectric surface upon which radiations reflected from said object are caused to impinge, for setting up an image current, said electronic means comprising a linearmosaic target.

4. The combination as in claim 3 and being further characterized in that said electron discharge device comprises means for generating a beam of electrons which moves in a direction perpendicular to the movement of said moving sheet of light. I v

5. In combination, a photoelectric cathode, means including means for'setting up a moving sheet of light for projecting an'image of an object so illuminated upon said cathode to generate a moving sheet of electrons, a linear target upon which electrons from said cathode impinge, means for generating a beam of electrons, and

'means for scanning said linear target along the length thereof with said beam of electrons.

6. In combination, means for illuminating succes'sively various linear portions of an object with a moving sheet of light, a photoelectric cathode, means for projecting an image of said 'object so illuminated upon said cathode as said portions 'of the object are successively illuminated to generate a moving sheet of electrons, means for generating a beam of electrons, a linear target upon which electrons from said cathode impinge, and' means for scanning said linear target along the length thereof with said beam of electrons, said linear target comprising a plurality of conducting members insulated one from the other.

{7. In combination,'means for illuminating successively various linear portions of an object with a moving sheet of light, a photoelectric cathode, means for projecting an image of said object so illuminated upon said cathode as said portions of the object are successively illuminated to generate a moving sheet of electrons,

.means for generating a beam of electrons, a

linear target upon which electrons from said cathode impinge, and means for scanning said linear target along the length thereof with said beam of electrons, said linear target comprising a plurality of stacked plates, said plates being alternately conducting and insulating.

8. In combination, means for illuminating successively various linear portions of an object with a moving thin sheet of light, a photoelectric cathode, means for projecting an image of said object so illuminated upon said cathode as said portions of the object are successively illuminated to generate a moving sheet of electrons, a linear target, means comprising electron deflecting means for causing said sheet of electrons to impinge upon said target, means for generating a beam of electrons, and means for [scanning said linear target along the length thereof with said beam of electrons.

9. In combination, means for illuminating successively various linear portions of an object with a moving thin sheet of light. a photoelectric cathode, means for projecting an image of said object so illuminated upon said cathode as said portions of the object are successively illumiassure nated to generate a moving sheet of'electrons, a linear target upon which said electrons impinge, electrode means other than said target for accelerating said electrons toward said target,

means for generating a beam of electrons, and means for scanning said' linear target along the length thereof with said beam of electrons.

10. In combination, means for illuminating successively various linear portions of an object with a moving thin sheet of'light, a curved pho- 1 toelectrlc cathode, means for projecting an image of said object so illuminated upon said cathode as said portions of the object are successively illumlnated to generate a moving sheet of electrons, a linear target upon which said electrons impinge, means for accelerating said electrons towards said target, means for generating a beam of electrons, and means for scanning said linear target "along the length thereof with said beam of electrons, said accelerating means comprising a plurality, of electrode members which are placed at potentials which are respectively greater the greater the distance of the electrode member from the cathode.

11. In combination, means for illuminating successively various linear portions of an object with a moving thin sheet of light, a photoelectric cathode, means for projecting an image or said object so illuminated upon said cathode as said portions of the object are successively illumi-- nated to generate a moving sheet of electrons, a linear target upon which electrons from said cathode impinge, means for generating a beam of electrons, and means for scanning said linear target along the length thereof with said beam of electrons on the side of said target remote from said cathode.

' '12. .In combination, electronic means for illuminating successively various linear portions of an object with a moving thin sheet of light, a photoelectric cathode, means for projecting an image of said object so illuminated upon said of electrons, means including said curved cathode and said anode member for projecting an image of the illuminated portion of said cathode upon the slit in said anode, an electrode member close- 1y, adjacent said slit upon which the electrons impinge after passing through said slit, and means including said electrode member for set-. ting up image currents which may be used to reproducean image of the object.

16. In combination, means for illuminating successively various linear portions of an object with amoving sheet of light, a curved photoelectric cathode, an anode member having a linear slit therein, means for projecting an'image of said object so illuminated upon said cathode as said portions of the object are successively illuminated to generate a moving sheet of electrons, means including said curved cathode and said anode member for projectingan image of the illuminated portion of said cathode upon the slit in said anode, an electrode member closely adjacent said slit upon which the electrons impinge. after passing through said slit, and means for scanning said linear target along the length thereof and on the side thereof remote from said photoelectric cathode with a beam of electrons.

17. In combination, an electron discharge device comprising an evacuated container containing a linear cathode, a plurality of cylindrical electron lens elements for forming electrons generated from said cathode nto a narrow sheet of electrons, a fluorescent screen upon which for illuminating successively'various linear por- I tions of an object with said moving sheet of light, an electron discharge device for setting up an electronic current, said discharge device having cathode as said portions of the object-are successively illuminated to generate a moving sheet of electrons, a linear target upon which electrons from said cathode impinge, means for gen-- erating a beam of electrons, and means for scanning said linear target along the length thereof with said beam of electrons.

13. The combination of elements as in claim 12 in which said electronic means comprises an electron discharge device having acylindrical electron lens system therein for forming sheet of electrons.- t

14. In combination, an electron discharge-device comprising an evacuated container enclosing a linear cathode, cylindrical electron lens elements for forming the electrons emitted from said cathode into a thin sheet of electrons, a fluorescent screen upon which said sheet impinges, and means for deflecting said sheet in a direction across said screen which is transversesuccessively various linear portions of an object with a moving sheet of light, a curved photoelectric cathode, an anode member having a linear slit therein, means for projecting an image of said object so illuminated upon said cathode as said linear portions of the object are successively illuminated to generate a moving sheet a thin a cathode, means for forming an image ofsaid object upon said cathode line by line as the object is illuminated, and meanswithin said device for converting the resulting electronic current into image current representative at each instant of a single .elemental portion of an elemental line of said object.

18. In combination, means for illuminating successively various linear portions of an object to be televised with a moving sheet of light which moves across said object in a given direction, an electron discharge tube having a container which I has a cross-section in a plane perpendicular to the longitudinal-axis thereof which has a dimension in one direction greater than its dimension at right angles thereto, said tube comprising a photoelectric element in one portion ofsaid tube, which element is curved in such a way that it has an intercept in a plane parallel to the direction of scanning which'is curved and a substantially linear intercept in a plane perpendicular to said direction of seaming, a linear array of conducting elements in said tube between the portion thereof containing said photoelectric element and a second portion thereof, each of said elements being insulated from the others and each having a face in each of said two portions of said tube, electron focussing means for focussing the electrons from said photoelectric element upon said array of conductin elements. said focus being in onlyone direction and such as to leave unchanged the direction of movement of said electrons in a direction transverse to said line of scanning, and means for seaming said array of conducting elements in said second tential and generate thereby a television signal current.

19. Television apparatus comprisingmeans for generating a thin sheet of light and'sweeping it repeatedly in the same path across an object or object field which is being televised, the sweep movement being perpendicular to the sheet and its period being'not greater than the period of persistence of vision, the width of said sheet of light being not less than the width of said object or field, a light sensitive electric element, means for forming a strip of light on said element with light reflected from said object or field so that the light distribution along said strip at each instant corresponds to the reflecting power of said object or field along the strip thereof which is illuminated at that instant, and means including .said lightsensitive element for setting up an image current representative of the light-tone values of said object or field.

20. Television apparatus comprising means for generating a thin sheet of light and sweeping it repeatedly in the same path across an object or object field which is'being televised, the sweep movement being perpendicular to the sheet and its period being not greater than the period of persistence ofvision, the width of said sheet of light being not less than the width of said object or field, a light sensitive electric element, means for forming a strip of light on said element with light reflected from said object or field so that the light distribution along said strip at each instant corresponds to the reflecting power of said object or field along the strip thereof which is illuminated at that instant, means including said light sensitive element for storing electric charges corresponding respectively with the light-tone values of a row of elemental areas making up an elemental strip across said field, and means for dissipating said charges in succession and thereby setting up an image current varying in accordance with said charges taken in succession.

21. An electro-optical scanning system comprising means for generating a thin sheet of electrons, a luminescent screen upon which said sheet impinges to cause it to emit light, means for repeatedly deflecting said sheet across said screen perpendicularly to the long dimension of the cross section of said sheet, and optical means for producing and directing upon an object field to be scanned a moving thin sheet of light from the moving line source of light produced on said luminescent screen.

22. The combination of elements as in claim 15 characterized in that the means for projecting an image of the illuminated portion of the oathode upon the anode includes means for deflecting electrons in a direction parallel to the move- I ment of the sheet of light and at the same rate.

23. In combination, means for illuminating at each instant a single elemental strip of a field of view to be scanned with a moving sheet of light,

a photoelectric cathode, means for directing light from said illuminated strip and forming with it an illuminated strip on said cathode, means for forming the electrons emitted from said illuminated strip on the cathode into a thin sheet and causing it to set up a line series of electric charges proportional respectively to the light-tone values of the elemental areas of the illuminated strip of the field of view, cathode ray producing means, and means including the cathode ray for removing each of the stored charges after a period of time equal to that required for said sheet of light to move along said field a distance equal to the thickness of said sheet at said field.

' GORDON K. TEAL. 

